ISIS-2 Topside Sounder Average Ionogram over Kashima, Japan: KSH, Latitude 36, Longitude 141

These Ionograms were digitized from the original ISIS-2 7-Track Analog Telemetry Tapes using the Facilities of the former Data Evaluation Laboratory at the NASA/GSFC. This Data Restoration Project is headed by Dr. R.F. Benson (NASA/GSFC). Ionograms were digitized at the Rate of 40,000 16-bit samples/s. This Sample Rate is higher than the Nyquist Frequency of 30 kHz. The Sample Frequency of 40 kHz provides a Measurement every 25 µs corresponding to an Apparent Range Interval equal to 3.75 km from c*t/2, where c is the Speed of Light. Ionograms with this Sample Rate are designated as 'Full' Ionograms because they have the full 3.75 km Apparent-Range Resolution. The Ionograms used for most Analyses, and those available from CDAWeb, were produced by averaging every four Samples of the Sounder-Receiver Video Amplitude Output to yield an average Value every 100 µs corresponding to an Apparent-Range Resolution of 15 km. These Ionogram Files are referred to as 'Average' Files with Standard Resolution. Each Ionogram consists of a Fixed-Frequency Portion and a Swept-Frequency Portion. The Time Resolution between Ionograms is typically 14 or 22 s depending on the Frequency Sweep Range.

本数据集所包含的电离图（ionogram），系采用美国国家航空航天局戈达德航天飞行中心（NASA/GSFC）原数据评估实验室的设备，从原始ISIS-2卫星的7轨模拟遥测磁带数字化生成。本数据修复项目由R.F.本森博士（NASA/GSFC）牵头。本次电离图的数字化采样率为40000个16位采样每秒，该采样率高于30kHz的奈奎斯特频率（Nyquist Frequency）。40kHz的采样频率每25微秒即可生成一组测量值，根据公式c*t/2计算可得，其对应的视距间隔为3.75km，其中c为光速（Speed of Light）。采用该采样率的电离图被命名为'Full' 电离图（'Full' Ionogram），因其具备完整的3.75km视距分辨率。多数分析所用以及可从协调数据分析网站（CDAWeb）获取的电离图，均通过对测深接收机（Sounder-Receiver）视频振幅输出的每4个采样取平均得到：每100微秒生成一组平均值，对应的视距分辨率为15km。这类电离图文件被称为标准分辨率'Average' 文件（'Average' File）。每幅电离图均包含固定频段部分与扫频频段部分，两幅电离图之间的时间分辨率通常为14秒或22秒，具体取决于扫频范围。